1. Field of the Invention
The present invention relates to a generation method of generating data for a mask pattern to be used for an exposure apparatus, a storage medium, and an information processing apparatus.
2. Description of the Related Art
With the recent advances in micropatterning of semiconductor devices, it has become difficult for an exposure apparatus to transfer (resolve) a pattern. To keep pace with the micropatterning of semiconductor devices, the exposure apparatus adopts resolution enhanced techniques such as modified illumination and optical proximity correction (OPC) to optimize the mask pattern or the illumination shape (effective light source distribution) used to illuminate a mask. The illumination shape indicates a light intensity distribution formed on the pupil plane of an illumination optical system, and also indicates the angle distribution of light which illuminates a mask.
To optimize the illumination shape, a layout pattern (target pattern) for a device, an evaluation position for a transfer pattern (optical image), and an evaluation item (for example, the size, the DOF, or the exposure latitude) at the evaluation position are set. Next, the transfer pattern is calculated while changing the illumination shape, thereby obtaining the value (evaluation value) of the evaluation item at the evaluation position on the transfer pattern. The transfer pattern calculation and the evaluation value obtaining are repeated until the obtained evaluation value falls within a tolerance range or the number of changes in illumination shape reaches a predetermined number. The illumination shape is numerically represented by, for example, a function having inner σ and outer σ as its parameters (variables), which are optimized using, for example, the Monte Carlo method in annular illumination having a given intensity. Even when the same mask pattern is used, the transfer pattern varies with a variation in illumination shape. The transfer pattern, thus, deviates from the target pattern upon changing the illumination shape. Therefore, OPC is necessary to match the transfer pattern with the target pattern. OPC is done every time the illumination shape is changed or when the illumination shape is changed by a given amount. Note that OPC is limited to correction of the shape of the transfer pattern such as a line width, edge shift, and image shift, and cannot perform correction for resolution performance, such as the contrast of the image and a depth of focus, which is determined based on the effective light source distribution.
U.S. Pat. No. 6,563,566 proposes a technique of setting a pattern to be formed on a substrate (wafer), and calculating the mask pattern and illumination shape optimized by a mathematical approach. The technique disclosed in U.S. Pat. No. 6,563,566 analytically calculates solutions (mask pattern and illumination shape) instead of repeatedly performing calculation. Although the technique disclosed in U.S. Pat. No. 6,563,566 does not adopt OPC, the pattern to be formed on the substrate and the optimized mask pattern are different from each other, and thus this technique can be reckoned as an illumination shape optimization technique including mask pattern correction in a broad sense.
Furthermore, Japanese Patent Laid-Open Nos. 2009-93138 and 2009-94109 propose a technique of inserting an auxiliary pattern (a pattern which itself is not resolved) to a main pattern (a pattern which itself is resolved) to reduce the difference in resolution performance between a fine, dense pattern and an isolated pattern. The technique described in Japanese Patent Laid-Open Nos. 2009-93138 and 2009-94109 inserts an auxiliary pattern at the peak (Laplacian peak) position of an aerial image approximation with 2D-TCC.
The technique disclosed in U.S. Pat. No. 6,563,566 has a merit that it analytically calculates solutions, but needs to limit the evaluation item to the tilt of an optical image, and to limit the type of pattern to be formed on the substrate to one specific type. As described above, the technique described in U.S. Pat. No. 6,563,566 is impractical because it has a demerit of a small number of degrees of freedom.
On the other hand, the technique disclosed in Japanese Patent Laid-Open Nos. 2009-93138 and 2009-94109 sets, for the known illumination shape, a fixed generation condition under which an auxiliary pattern is generated, that is, a method of inserting an auxiliary pattern. The technique described in Japanese Patent Laid-Open Nos. 2009-93138 and 2009-94109 cannot always determine an optimum illumination condition and mask pattern.